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The Maxwell stress tensor and conservation of momentum are used to find the radiation reaction force on a point charge accelerating parallel to its velocity. The derived force, [Formula: see text], is quite different from the Abraham–Lorentz force. It does not depend on the time derivative of the acceleration, and has none of the problems associated with the Abraham–Lorentz force.

A point charge accelerating under the influence of an external force emits electromagnetic radiation that reduces the increase in its mechanical energy. This causes a reduction in the particle’s acceleration. We derive the decrease in acceleration due to radiation reaction for a particle accelerating parallel to its velocity, and show that it has a negligible effect.

In quantum mechanics, the magnetic field has a physical effect beyond its local presence. For axially symmetric vector potentials, A = A ( s , z ) ϕ , it is the magnetic flux that plays a central role in both interference experiments (as in the Aharonov-Bohm effect) and in bound state spectra for a particle constrained to move in a circle. The flux dependence is evident in various configurations, and we have chosen two applications to highlight the non-local nature of the quantum mechanical magnetic field dependence: A finite solenoid and a Dirac string with a non-zero radius. The finite solenoid is interesting because it represents the actual experimental apparatus for measuring the Aharonov-Bohm effect. The Dirac string provides an electric charge quantization mechanism that depends on where the quantization argument is applied, yielding different fundamental charge units for different locations.

We developed two virtual reality demonstrations for electromagnetism. For statics, we use spherical building blocks and superposition to calculate the electric field of a user-generated configuration of charge. The electric field information is displayed on a three-dimensional grid using vector arrows. A second demonstration displays field information for electromagnetic fields generated by a particle moving along a user-generated path (at arbitrary speed). We used the Unity game creation engine to efficiently develop the demonstrations, and tested them on an HTC Vive VR headset with handheld controllers.

We discuss an extension of the velocity Verlet method that accurately approximates the kinetic-energy-conserving charged particle motion that comes from magnetic forcing. For a uniform magnetic field, the method is shown to conserve both particle kinetic energy and magnetic dipole moment better than midpoint Runge-Kutta. We then use the magnetic velocity Verlet method to generate trapped particle trajectories, both in a cylindrical magnetic mirror machine setup, and for dipolar fields like the earth's magnetic field. Finally, the method is used to compute an example of (single) mirror motion in the presence of a magnetic monopole field, where the trajectory can be described in closed form., To appear, American Journal of Physics

Properties of b-baryon decay matrix elements (amplitudes) have been derived in a nonsymmetric quark model without any use of SU(6), SU(3), or SU(2) (isotopic spin) groups. Equalities between pairs of amplitudes are derived, and $\Lambda-\Sigma$ mixing is used to calculate the branching ratio for the transition $\Lambda_b\rightarrow \Sigma^0$., Comment: The derivation has been simplified

We show that the attack on my paper, “Complete Lorentz transformation of a charge-current density,” by Kholmetskii, Missevitch, and Yarman in their paper, “Lorentz transformation of a charge-current density and ‘relativistic polarization’ of a moving current loop” is based on completely erroneous assumptions and equations.

It is generally assumed in the literature that a Lorentz transformation on a neutral current loop results in a moving current loop with a nonvanishing charge distribution and an electric dipole moment. We show in this paper that this is not, in fact, correct. The derivation that leads to the charge distribution was based on an incomplete Lorentz transformation, which transforms the charge-current four-vector $j^\mu=[\rho({\bf r},t),{\bf j(r},t)]$, but not the space-time four-vector $x^\mu=(t,{\bf r})$. We show that completing the Lorentz transformation by using the variable $t'$ in the moving frame, rather than keeping the rest frame time variable $t$, results in there being no induced charge density and no resulting electric dipole moment., Comment: This version has added some new discussion, and included a new reference. This version has been published in International Journal of Modern Physics A Vol. 35,2050061 (2020)

The origin of electromagnetic momentum for general static charge-current distributions is examined. The electromagnetic momentum for static electromagnetic fields is derived by implementing conservation of momentum for the sum of mechanical momentum and electromagnetic momentum. The external force required to keep matter at rest during the production of the final static configuration produces the electromagnetic momentum. Examples of the electromagnetic momentum in static electric and magnetic fields are given. The `center of energy' theorem is shown to be violated by electromagnetic momentum. `Hidden momentum' is shown to be generally absent, and not to cancel electromagnetic momentum., Comment: Extended the discussion with some addition to the results, and no change in the conclusions

We show that attempts to modify the force on a magnetic dipole by introducing either hidden momentum or internal forces are not correct. The standard textbook result ${\bf F=\nabla(\bmu\cdot B)}$ is correct even in the presence of time dependent electromagnetic fields. Using this expression for the force, overall momentum (the sum of mechanical and electromagnetic momentum) is conserved in changing electromagnetic fields., This version presents a more compelling argument that the textbook equation for the force on a magnetic dipole is correct, and is needed to preserve overall momentum conservation

We show that the conclusion in the paper (Kholmetskii and Yarman 2008 Eur. J. Phys. 29 1135–46) that there is a paradox in Poynting's theorem for a moving charged particle is wrong. Contrary to the claim in their paper, there is no need to modify the standard form of the Poynting vector for this case, and their proposed modification is wrong.

The absence of any tendency toward rotation in a moving right angle lever is given a simple explanation., Comment: Appendix added with discussion of previous interpretations. To be published in European Journal of Physics

The absence of any tendency toward rotation in the Trouton-Noble experiment is given a simple explanation., Comment: The derivations have been extended to more general cases. Title has been changed

A general three quark bound state satisfying the Pauli principle, and conserving angular momentum and isospin, is used to investigate the spin structure of nucleons at high $x$. It is shown if {$F_{1n}/F_{1p}$$\to$1/4}, then both $A_{1p}$ and $A_{1n}$, as well as quark spin distribution $\Delta u/u$, will approach 1 as $x$$\to$1 in polarized deep inelastic scattering. The spin distribution $\Delta d/d$ does not approach 1, but is bound by the limits $-{1/3}\le\Delta d/d\le 0$ for any $x$., Comment: The quark function \phi(123) satisfies the constraint \phi(123)+\phi(213)=\phi(132)+\phi(231), which is less restrictive than the symmetry condition \phi(123)=\phi(132) originally stated. This means the constraint d\downarrow=u\uparrow does not hold at all x. (It still applies for x--> 1.) The main conclusions that \Delta u/u--> 1 as x--> 1, but -1/3

We find the electric field of a point charge in `truncated hyperbolic motion', in which the charge moves at a constant velocity followed by motion with a constant acceleration in its instantaneous rest frame. The same Lienard-Wiechert formula holds for the acceleration phase and the constant velocity phase of the charge's motion. The only modification is that the formula giving the retarded time is different for the two motions, and the acceleration is zero for the constant velocity motion. The electric field lines are continuous as the retarded time increases through the transition time between constant velocity and accelerated motion. As the transition time approaches negative infinity the electric field develops a delta function contribution that has been introduced by others as necessary to preserve Gauss's law for the electric field., Comment: The discussion has been modified and some equations added, with no change in the results or the figures

We consider the one-dimensional motion of a particle randomly accelerated by Gaussian white noise on the line segment $0lxl1.$ The reflections of the particle from the boundaries at $x=0,1$ are inelastic. The velocities just before and after reflection are related by ${v}_{f}=\ensuremath{-}{\mathrm{rv}}_{i},$ where r is the coefficient of restitution. Cornell, Swift, and Bray [Phys. Rev. Lett. 81, 1142 (1998)] have argued that there is an inelastic collapse transition in this system. For $rg{r}_{c}{=e}^{\ensuremath{-}\ensuremath{\pi}/\sqrt{3}}$ the particle moves throughout the interval $0lxl1,$ while for $rl{r}_{c}$ the particle is localized at $x=0$ or $x=1.$ In this paper the equilibrium distribution function $P(x,v)$ is analyzed for $rg{r}_{c}$ by solving the steady-state Fokker-Planck equation, and the results are compared with numerical simulations.

We have performed an experimental investigation of equilibration between edge states in the fractional quantum Hall regime. We have developed a technique to alter the electrostatic potential at the edge continuously and controllably from a smooth to a sharp potential gradient, using a set of gates. A non-equilibrium current distribution in the edge states is created which then travels along the edge to a detector. The scattering between the various fractional edge states is investigated, and a method developed to calculate scattering probabilities between pairs of edge states, revealing independent 1 5 , 1 3 and 2 5 edge states, for a bulk filling factor of 2/3. Equilibration is found to depend strongly on the potential slope.

The masses of the ground-state baryons are calculated in a relativistic quark model by using the saddle-point variational method to solve the three-body Breit equation. The saddle-point variational method maximizes the energy with respect to small component parameters, while minimizing with respect to size parameters. This removes the problems usually caused by negative-energy states, without the need for positive-energy projection operators. The variational method, applied to an asymmetric trial wave function with naturally borken SU(3) and SU(6) symmetry, permits solution of the Breit equation for realistic QCD-inspired potentials without using perturbation theory. The calculated masses are in good agreement with experiment, and the asymmetric wave function gives reasonable values for the proton and neutron charge radii.

We have investigated experimentally resonant tunnelling through single-particle states formed around an antidot by a magnetic field, in the fractional quantum Hall regime. For 1/3 filling factor around the antidot, Aharonov-Bohm oscillations are observed with the same magnetic field period as in the integer quantum Hall regime. All our measurements are consistent with quasiparticles of fractional charge e*. However, the results are also consistent with particles of any charge (>= e*) as the system must rearrange every time the flux enclosed increases by h/e., Postscript, 4 pages, gzipped (350 kB)

We study the acceleration and collisions of rigid bodies in special relativity. After a brief historical review, we give a physical definition of the term `rigid body' in relativistic straight line motion. We show that the definition of `rigid body' in relativity differs from the usual classical definition, so there is no difficulty in dealing with rigid bodies in relativistic motion. We then describe: 1. The motion of a rigid body undergoing constant acceleration to a given velocity. 2. The acceleration of a rigid body due to an applied impulse. 3. Collisions between rigid bodies., Extended the discussion,and added references

In a recent letter, several electromagnetic mass difference formulae for baryons were presented. However, because the derivation did not include important colormagnetic terms, the mass relations do not correctly give isospin mass splittings for the baryons. Correct mass formulae were published some time ago in a model independent approach that was more general and correct than the approach in this letter. In this Comment, the errors in the letter are pointed out and some correct formulae presented., Comment on arXiv:1009.5250 by Yang, Kim, Polyakov

We show that the conclusion of a recent experiment [arXiv:0912.3934] that claims to have discovered that "the speed of light seems to depend on the motion of the observer" is wrong., 4 pages

The meaning of Lorentz contraction in special relativity and its connection with Bell's spaceships parable is discussed. The motion of Bell's spaceships is then compared with the accelerated motion of a rigid body. We have tried to write this in a simple form that could be used to correct students' misconceptions due to conflicting earlier treatments., Modified the discussion in Sec. 2. This version to be published in European Journal of Physics

Proton-proton bremsstrahlung calculations are compared to the 280-MeV experimental results from TRIUMF, which use a polarized proton beam. Calculations are included for all experimental results. The Bonn radial potential is compared to a modified Hamada-Johnston and the Bryan-Gersten potentials. Potentials with different short-range radial behavior are compared in order to examine the penetration of the photon radiation. Rather good agreement with experiment for the Bonn potential is achieved without the arbitrary normalization of 2/3 applied to the TRIUMF cross-section data. The rescattering included in our work accounts for an increase of up to approximately 20% in the cross section, which is not large enough to explain the differences with other calculations, and it contributes up to a factor of 2.5 in the analyzing power. Our present results include partial waves up to {ital J}{sub max}=6.

The authors argue that it is inappropriate to use SU(3) flavour symmetry in analysing the recent EMC measurement of the proton spin structure function and then present a light-cone, quark-proton model analysis without using SU(3). The nucleon is described as a bound state of three relativistic quarks on the light-cone. The constituent quarks have their own internal structure in terms of valence quarks, a quark-antiquark sea and gluons. The EMC result, taken in conjunction with the Bjorken sum rule, gives, separately, the valence quark and an effective sea contribution to the proton spin, demonstrating explicit cancellation of the valence and sea contributions.

A simple analytical solution is found to the Dirac equation for the combination of a Coulomb potential with a linear confining potential. An appropriate linear combination of Lorentz scalar and vector linear potentials, with the scalar part dominating, can be chosen to give a simple Dirac wave function. The binding energy depends only on the Coulomb strength, and is not affected by the linear potential. The method works for the ground state, or for the lowest state with $l=j-{1/2}$, for any $j$., Misprints (mostly of sign) corrected in equations (8), (9), (13), (14), (18), and (21). No change in results or discussion

Model independent sum rules for heavy baryon masses are tested for baryons containing charmed or bottom quarks. The sum rules depend only on the assumption that baryon mass differences are determined by spin-dependent two-body energies of quark pairs that do not depend on which baryon the quark pair is in. No assumption is made about the details of the quark-quark interaction. The sum rules are generally well satisfied, although better experimental accuracy would be required for a quantitative test of some of the sum rules. The success of the sum rules is evidence that "baryon independence" of quark-quark interaction is a good assumption for baryon mass calculations. It also means that the success of some detailed baryon mass calculations may not depend on the specific mechanism used in the calculation.

We explore the possibility of diquark clustering as a source of the asymmetry in the quark distribution amplitudes found by the QCD sum-rule technique. We consider a simple light-cone wave-function model for the nucleon and find that a two-quark correlation in the spin-zero state provides a significantly better account of the Chernyak-Zhitnitsky asymmetry than does a previous symmetric quark model with uncorrelated quarks.

A general three quark bound state satisfying the Pauli principle, and conserving angular momentum and isospin, is used to investigate the spin structure of nucleons at high $x$. It is shown that, if a spin up quark dominates as $x$$\to$1 for a spin up proton, it must be a u quark. Then both $A_{1p}$ and $A_{1n}$, as well as the quark spin distribution $\Delta u/u$, will approach 1 as $x$$\to$1. The spin distribution $\Delta d/d$ does not approach 1, but is bound by the limits $-{1/3}\le\Delta d/d\le 0$ for any $x$. The ratio {$F_{1n}/F_{1p}$ will approach 1/4} (not3/7)., Comment: Presented at HIX 2004, Marseille July 23-26, 2004

Baryon magnetic moments and beta decay ratios ($G_A/G_V$) are calculated in a phenomenological quark model. Non-static effects of pion exchange and orbital excitation are included. Good agreement with experiment is found for a combined fit to all measured baryon magnetic moments and beta decay ratios. The model predicts an antiquark content for the proton that is consistent with the Gottfried sum rule., Comment: 14 pages in LaTex

We show that a form for the second partial derivative of 1/r proposed by Frahm and subsequently used by other workers applies only when averaged over smooth functions. We use dyadic notation to derive a more general form without that restriction.

Exact analytic solutions are found to the Dirac equation for a combination of Lorentz scalar and vector Coulombic potentials with additional non-Coulombic parts. An appropriate linear combination of Lorentz scalar and vector non-Coulombic potentials, with the scalar part dominating, can be chosen to give exact analytic Dirac wave functions., Comment: 4 pages. No figures. Presented in Hadron 2000: International Workshop on Hadron Physics, Caraguatatuba, SP, Brasil, April 2000

Exact solutions are found to the Dirac equation for a combination of Lorentz scalar and vector Coulombic potentials with additional non-Coulombic parts. An appropriate linear combination of Lorentz scalar and vector non-Coulombic potentials, with the scalar part dominating, can be chosen to give exact analytic Dirac wave functions. The method works for the ground state or for the lowest orbital state with l=j-{1/2}, for any j., Comment: 7 pages, Latex file

New experimental measurements are used to test model independent sum rules for charmed baryon masses. Sum rules for medium-strong mass differences are found to be reasonably well satisfied with increasing accuracy, and the new measurements permit an improved prediction of $2778\pm 9$ MeV for the mass of the $\Omega_c^{*0}$. But an isospin breaking sum rule for the $\Sigma_c$ mass splittings is still in significant disagreement posing a serious problem for the quark model of charmed baryons. Individual $\Sigma_c$ mass splittings are investigated, using the new CLEO measurement of the $\Xi_c^\prime$ mass splitting, but the accuracy is not yet sufficient for a good test., Comment: 6 pages, latex, no figures

The importance of exchange currents, and of conserving isotopic spin at both the quark and baryon levels in application of the chiral quark model to any calculation of baryon magnetic moments is emphasized., Comment: 5 pages, Latex file

Model independent sum rules are applied to recent measurements of heavy c-baryon and d-baryon masses. The sum rules are generally satisfied to the same degree as for the light (u,d,s) baryons., 5 pages Latex. The replacement clarifies the discussion on the first two pages

A rest frame valence quark model is applied to the deep inelastic scattering of charged leptons by protons. The parameters of the model are determined by a fit to unpolarized electron cross sections. The model then can be used to calculate the asymmetry in polarized deep inelastic scattering. The predicted spin-dependent structure function g1p is in good agreement with recent measurements. This indicates that, in the proton rest system, the spin of the proton is carried by the valence quarks., 22 pages, Latex file with 10 uuencoded tar compressed PostScript figures

The measured masses of the three charge states of the charmed $\Sigma_c$ baryon are found to be in disagreement with a sum rule based on the quark model, but relying on no detailed assumptions about the form of the interaction. This poses a significant problem for the charmed baryon sector of the quark model. Other relations among charmed baryon masses are also discussed., Comment: 5 pages, latex, no figures

Electron-proton deep inelastic scattering is treated as the incoherent scattering of electrons by bound Dirac partons in the proton rest frame. An approximate bound state wave function is used for the initial parton, while the final parton is considered free. A good fit is obtained to the structure function F1(x,Q2) in the range x > 0.15, Q2 > 2 GeV. The subsequent prediction for F2(x,Q2) is not as good, indicating a small additional contribution by longitudinal photons for W < 2.5 GeV. The parton momentum distribution is found to contain transverse momentum of 400–600 MeV, increasing with x.

Symmetrized, forward dispersion relations with good convergence properties are used to provide a unitary extrapolation of the Weinberg (current algebra) amplitudes to the physical low-energy region. The extrapolated phase shifts tend to agree with experiment up to about 550 MeV. The dispersion integral unitarization increases Weinberg's $I=0$ scattering length from 0.21 to 0.24. We show that attempts to extrapolate data from above 400 MeV down to threshold using the effective-range formula lead to spurious (high) estimates of the Weinberg scattering lengths. A true test of the Weinberg hypothesis would require consistent data around 325 MeV.